1. Field of Invention
This invention relates to radar and more particularly to a radar that provides a beam which continuously scans a partial region.
2. Description of the Prior Art
In a military operation on land, it is usually desirable to have a radar that is mobile, light, small and thereby suitable for deployment near a battlefield. As known to those skilled in the art, most of the weight and bulk of the radar is in the antenna of the radar. A fixedly mounted antenna, such as a phased array antenna, is not suitable for deployment near the battlefield because radiating elements of the phased array antenna are heavy and bulky.
One type of radar, designed for use in the military operation on land, has a paraboloid reflector antenna that typically includes a plurality of radiators disposed in an elevation sector near the focal point of a paraboloid reflector. The radiators and the reflector are mounted on a platform that is rotatable about an azimuth axis. When excitation is applied to a radiator, energy therefrom is transmitted to the reflector. The energy is reflected from the reflector, thereby providing a single beam of energy that propagates through a spatial region. The angle of elevation of the beam is related to the position of the excited radiator. The azimuth of the beam is selected by rotating the platform about the azimuth axis.
A sequential application of excitation to the radiators causes the radiators to provide a scan beam that continuously scans the spatial region in elevation. The scan beam continuously scans the spatial region in azimuth and elevation when the platform is rotated about the azimuth axis during the sequential application of excitation.
Usually, the apparatus for sequentially exciting the radiators is costly and complex. Moreover, the scan beam may have an undesired lack of uniformity during the sequential application of excitation. Additionally, the sequential application of excitation may cause an undesired spurious excitation of some of the radiators. The spurious excitation causes large, unwanted side lobes in a far field pattern of the paraboloid reflector antenna along with a wider beamwidth.